Handing off an access terminal during a multicast session within a wireless communications system

ABSTRACT

Methods and apparatuses for multicasting within a wireless communications system are disclosed. In one embodiment a method of multicasting within a wireless communications system operating in accordance with a given wireless communication protocol includes monitoring multicast messages associated with a given multicast session in a first sector. A handoff occurs from the first sector to a second sector. It is determined whether the second sector is transmitting multicast messages associated with the given multicast session. Then, based on the determination, a registration request for the given multicast session within the second sector is transmitted on a reverse link access channel in an earlier slot than a next designated slot for registration requests as defined by the wireless communication protocol.

CLAIM OF PRIORITY

The present Application for Patent is a Divisional of Non-Provisionalapplication Ser. No. 12/751,675, entitled “HANDING OFF AN ACCESSTERMINAL DURING A MULTICAST SESSION WITHIN A WIRELESS COMMUNICATIONSSYSTEM”, filed on Mar. 31, 2010, which in turn claims priority toProvisional Application No. 61/168,855 entitled “HANDING OFF AN ACCESSTERMINAL DURING A MULTICAST SESSION WITHIN A WIRELESS COMMUNICATIONSSYSTEM” filed Apr. 13, 2009, and assigned to the assignee hereof andhereby expressly incorporated by reference herein.

BACKGROUND

1. Field

Embodiments are directed to multicasting within a wirelesscommunications system, and more particularly to handing off an accessterminal during a multicast session within the wireless communicationssystem.

2. Description of the Related Art

Wireless communication systems have developed through variousgenerations, including a first-generation analog wireless phone service(1G), a second-generation (2G) digital wireless phone service (includinginterim 2.5G and 2.75G networks) and a third-generation (3G) high speeddata/Internet-capable wireless service. There are presently manydifferent types of wireless communication systems in use, includingCellular and Personal Communications Service (PCS) systems. Examples ofknown cellular systems include the cellular Analog Advanced Mobile PhoneSystem (AMPS), and digital cellular systems based on Code DivisionMultiple Access (CDMA), Frequency Division Multiple Access (FDMA), TimeDivision Multiple Access (TDMA), the Global System for Mobile access(GSM) variation of TDMA, and newer hybrid digital communication systemsusing both TDMA and CDMA technologies.

The method for providing CDMA mobile communications was standardized inthe United States by the Telecommunications IndustryAssociation/Electronic Industries Association in TIA/EIA/IS-95-Aentitled “Mobile Station-Base Station Compatibility Standard forDual-Mode Wideband Spread Spectrum Cellular System,” referred to hereinas IS-95. Combined AMPS & CDMA systems are described in TIA/EIA StandardIS-98. Other communications systems are described in the IMT-2000/UM, orInternational Mobile Telecommunications System 2000/Universal MobileTelecommunications System, standards covering what are referred to aswideband CDMA (WCDMA), CDMA2000 (such as CDMA2000 1xEV-DO standards, forexample) or TD-SCDMA.

In wireless communication systems, mobile stations, handsets, or accessterminals (AT) receive signals from fixed position base stations (alsoreferred to as cell sites or cells) that support communication links orservice within particular geographic regions adjacent to or surroundingthe base stations. Base stations provide entry points to an accessnetwork (AN)/radio access network (RAN), which is generally a packetdata network using standard Internet Engineering Task Force (IETF) basedprotocols that support methods for differentiating traffic based onQuality of Service (QoS) requirements. Therefore, the base stationsgenerally interact with ATs through an over the air interface and withthe AN through Internet Protocol (IP) network data packets.

In wireless telecommunication systems, Push-to-talk (PTT) capabilitiesare becoming popular with service sectors and consumers. PTT can supporta “dispatch” voice service that operates over standard commercialwireless infrastructures, such as CDMA, FDMA, TDMA, GSM, etc. In adispatch model, communication between endpoints (ATs) occurs withinvirtual groups, wherein the voice of one “talker” is transmitted to oneor more “listeners.” A single instance of this type of communication iscommonly referred to as a dispatch call, or simply a PTT call. A PTTcall is an instantiation of a group, which defines the characteristicsof a call. A group in essence is defined by a member list and associatedinformation, such as group name or group identification.

Conventionally, data packets within a wireless communications networkhave been configured to be sent to a single destination or accessterminal. A transmission of data to a single destination is referred toas “unicast”. As mobile communications have increased, the ability totransmit given data concurrently to multiple access terminals has becomemore important. Accordingly, protocols have been adopted to supportconcurrent data transmissions of the same packet or message to multipledestinations or target access terminals. A “broadcast” refers to atransmission of data packets to all destinations or access terminals(e.g., within a given cell, served by a given service provider, etc.),while a “multicast” refers to a transmission of data packets to a givengroup of destinations or access terminals. In an example, the givengroup of destinations or “multicast group” may include more than one andless than all of possible destinations or access terminals (e.g., withina given group, served by a given service provider, etc.). However, it isat least possible in certain situations that the multicast groupcomprises only one access terminal, similar to a unicast, oralternatively that the multicast group comprises all access terminals(e.g., within a cell or sector), similar to a broadcast.

Broadcasts and/or multicasts may be performed within wirelesscommunication systems in a number of ways, such as performing aplurality of sequential unicast operations to accommodate the multicastgroup, allocating a unique broadcast/multicast channel (BCH) forhandling multiple data transmissions at the same time and the like. Aconventional system using a broadcast channel for push-to-talkcommunications is described in United States Patent ApplicationPublication No. 2007/0049314 dated Mar. 1, 2007 and entitled“Push-To-Talk Group Call System Using CDMA 1x-EVDO Cellular Network”,the contents of which are incorporated herein by reference in itsentirety. As described in Publication No. 2007/0049314, a broadcastchannel can be used for push-to-talk calls using conventional signalingtechniques. Although the use of a broadcast channel may improvebandwidth requirements over conventional unicast techniques, theconventional signaling of the broadcast channel can still result inadditional overhead and/or delay and may degrade system performance.

The 3^(rd) Generation Partnership Project 2 (“3GPP2”) defines abroadcast-multicast service (BCMCS) specification for supportingmulticast communications in CDMA2000 networks. Accordingly, a version of3GPP2's BCMCS specification, entitled “CDMA2000 High RateBroadcast-Multicast Packet Data Air Interface Specification”, dated Feb.14, 2006, Version 1.0 C.S0054-A, is hereby incorporated by reference inits entirety.

SUMMARY

Embodiments are directed to methods and apparatuses for multicastingwithin a wireless communications system, and more particularly tohanding off an access terminal during a multicast session within thewireless communications system. In one embodiment a method ofmulticasting within a wireless communications system operating inaccordance with a given wireless communication protocol includesmonitoring multicast messages associated with a given multicast sessionin a first sector. A handoff occurs from the first sector to a secondsector. It is determined whether the second sector is transmittingmulticast messages associated with the given multicast session. Then,based on the determination, a registration request for the givenmulticast session within the second sector is transmitted on a reverselink access channel in an earlier slot than a next designated slot forregistration requests as defined by the wireless communication protocol.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of embodiments and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings which arepresented solely for illustration and not limitation of the embodiments,and in which:

FIG. 1 is a diagram of a wireless network architecture that supportsaccess terminals and access networks in accordance with at least oneembodiment.

FIG. 2 illustrates the carrier network according to an exampleembodiment.

FIG. 3 is an illustration of an access terminal in accordance with atleast one embodiment.

FIG. 4A illustrates a multicast call-setup process for a multicastsession to be carried on a downlink broadcast channel (BCH) in bothtarget and supporting sectors according to an embodiment.

FIG. 4B illustrates a cluster formed during the process of FIG. 4A.

FIG. 5A illustrates a multicast call-setup process for a multicastsession to be carried on the downlink BCH in one or more target sectorsaccording to an embodiment.

FIG. 5B illustrates an example of a cluster of sectors that may begenerated to support the multicast session during the process of FIG. 5Aaccording to an embodiment.

FIG. 6A illustrates BCH setup in a non-target sector for an activemulticast session after the process of FIG. 5A according to anembodiment.

FIG. 6B illustrates a portion of the example cluster from FIG. 5B duringthe process of FIG. 6A according to an embodiment.

FIG. 6C illustrates an updated version of the example cluster from FIG.5B after access terminal migration from a target sector to a non-targetsector during the process of FIG. 6A according to an embodiment.

FIG. 7 illustrates BCH setup in a non-target sector for an activemulticast session after the process of FIG. 5A according to anotherembodiment.

FIG. 8 illustrates BCH setup in a non-target sector for an activemulticast session after the process of FIG. 5A according to yet anotherembodiment.

FIG. 9A illustrates BCH setup in a target sector for an active multicastsession after the process of FIG. 5A according to an embodiment.

FIG. 9B illustrates a portion of the example cluster from FIG. 5B duringthe process of FIG. 9A according to an embodiment.

FIG. 9C illustrates an updated version of the example cluster from FIG.5B after access terminal migration between target sectors during theprocess of FIG. 9A according to an embodiment.

DETAILED DESCRIPTION

Aspects are disclosed in the following description and related drawingsdirected to specific embodiments. Alternate embodiments may be devisedwithout departing from the scope of the embodiments. Additionally,well-known elements of the embodiments will not be described in detailor will be omitted so as not to obscure the relevant details of theembodiments.

The words “exemplary” and/or “example” are used herein to mean “servingas an example, instance, or illustration.” Any embodiment describedherein as “exemplary” and/or “example” is not necessarily to beconstrued as preferred or advantageous over other embodiments. Likewise,the term “embodiments” does not require that all embodiments include thediscussed feature, advantage or mode of operation.

Further, many embodiments are described in terms of sequences of actionsto be performed by, for example, elements of a computing device. It willbe recognized that various actions described herein can be performed byspecific circuits (e.g., application specific integrated circuits(ASICs)), by program instructions being executed by one or moreprocessors, or by a combination of both. Additionally, these sequence ofactions described herein can be considered to be embodied entirelywithin any form of computer readable storage medium having storedtherein a corresponding set of computer instructions that upon executionwould cause an associated processor to perform the functionalitydescribed herein. Thus, the various aspects of the embodiments may beembodied in a number of different forms, all of which have beencontemplated to be within the scope of the claimed subject matter. Inaddition, for each of the embodiments described herein, thecorresponding form of any such embodiments may be described herein as,for example, “logic configured to” perform the described action.

A High Data Rate (HDR) subscriber station, referred to herein as anaccess terminal (AT), may be mobile or stationary, and may communicatewith one or more HDR base stations, referred to herein as modem pooltransceivers (MPTs) or base stations (BS). An access terminal transmitsand receives data packets through one or more modem pool transceivers toan HDR base station controller, referred to as a modem pool controller(MPC), base station controller (BSC) and/or packet control function(PCF). Modem pool transceivers and modem pool controllers are parts of anetwork called an access network. An access network transports datapackets between multiple access terminals.

The access network may be further connected to additional networksoutside the access network, such as a corporate intranet or theInternet, and may transport data packets between each access terminaland such outside networks. An access terminal that has established anactive traffic channel connection with one or more modem pooltransceivers is called an active access terminal, and is said to be in atraffic state. An access terminal that is in the process of establishingan active traffic channel connection with one or more modem pooltransceivers is said to be in a connection setup state. An accessterminal may be any data device that communicates through a wirelesschannel or through a wired channel, for example using fiber optic orcoaxial cables. An access terminal may further be any of a number oftypes of devices including but not limited to PC card, compact flash,external or internal modem, or wireless or wireline phone. Thecommunication link through which the access terminal sends signals tothe modem pool transceiver is called a reverse link or traffic channel.The communication link through which a modem pool transceiver sendssignals to an access terminal is called a forward link or trafficchannel. As used herein the term traffic channel can refer to either aforward or reverse traffic channel.

FIG. 1 illustrates a block diagram of one exemplary embodiment of awireless system 100 in accordance with at least one embodiment. System100 can contain access terminals, such as cellular telephone 102, incommunication across an air interface 104 with an access network orradio access network (RAN) 120 that can connect the access terminal 102to network equipment providing data connectivity between a packetswitched data network (e.g., an intranet, the Internet, and/or carriernetwork 126) and the access terminals 102, 108, 110, 112. As shown here,the access terminal can be a cellular telephone 102, a personal digitalassistant 108, a pager 110, which is shown here as a two-way text pager,or even a separate computer platform 112 that has a wirelesscommunication portal. Embodiments can thus be realized on any form ofaccess terminal including a wireless communication portal or havingwireless communication capabilities, including without limitation,wireless modems, PCMCIA cards, personal computers, telephones, or anycombination or sub-combination thereof. Further, as used herein, theterms “access terminal”, “wireless device”, “client device”, “mobileterminal” and variations thereof may be used interchangeably.

Referring back to FIG. 1, the components of the wireless network 100 andinterrelation of the elements of the exemplary embodiments are notlimited to the configuration illustrated. System 100 is merely exemplaryand can include any system that allows remote access terminals, such aswireless client computing devices 102, 108, 110, 112 to communicateover-the-air between and among each other and/or between and amongcomponents connected via the air interface 104 and RAN 120, including,without limitation, carrier network 126, the Internet, and/or otherremote servers.

The RAN 120 controls messages (typically sent as data packets) sent to abase station controller/packet control function (BSC/PCF) 122. TheBSC/PCF 122 is responsible for signaling, establishing, and tearing downbearer channels (i.e., data channels) between a packet data service node160 (“PDSN”) and the access terminals 102/108/110/112. If link layerencryption is enabled, the BSC/PCF 122 also encrypts the content beforeforwarding it over the air interface 104. The function of the BSC/PCF122 is well-known in the art and will not be discussed further for thesake of brevity. The carrier network 126 may communicate with theBSC/PCF 122 by a network, the Internet and/or a public switchedtelephone network (PSTN). Alternatively, the BSC/PCF 122 may connectdirectly to the Internet or external network. Typically, the network orInternet connection between the carrier network 126 and the BSC/PCF 122transfers data, and the PSTN transfers voice information. The BSC/PCF122 can be connected to multiple base stations (BS) or modem pooltransceivers (MPT) 124. In a similar manner to the carrier network, theBSC/PCF 122 is typically connected to the MPT/BS 124 by a network, theInternet and/or PSTN for data transfer and/or voice information. TheMPT/BS 124 can broadcast data messages wirelessly to the accessterminals, such as cellular telephone 102. The MPT/BS 124, BSC/PCF 122and other components may form the RAN 120, as is known in the art.However, alternate configurations may also be used and the embodimentsare not limited to the configuration illustrated. For example, inanother embodiment the functionality of the BSC/PCF 122 and one or moreof the MPT/BS 124 may be collapsed into a single “hybrid” module havingthe functionality of both the BSC/PCF 122 and the MPT/BS 124.

FIG. 2 illustrates the carrier network 126 according to an embodiment.In the embodiment of FIG. 2, the carrier network 126 includes a packetdata serving node (PDSN) 160, a broadcast serving node (BSN) 165, anapplication server 170 and an Internet 175. However, application server170 and other components may be located outside the carrier network inalternative embodiments. The PDSN 160 provides access to the Internet175, intranets and/or remote servers (e.g., application server 170) formobile stations (e.g., access terminals, such as 102, 108, 110, 112 fromFIG. 1) utilizing, for example, a cdma2000 Radio Access Network (RAN)(e.g., RAN 120 of FIG. 1). Acting as an access gateway, the PDSN 160 mayprovide simple IP and mobile IP access, foreign agent support, andpacket transport. The PDSN 160 can act as a client for Authentication,Authorization, and Accounting (AAA) servers and other supportinginfrastructure and provides mobile stations with a gateway to the IPnetwork as is known in the art. As shown in FIG. 2, the PDSN 160 maycommunicate with the RAN 120 (e.g., the BSC/PCF 122) via a conventionalA10 connection. The A10 connection is well-known in the art and will notbe described further for the sake of brevity.

Referring to FIG. 2, the broadcast serving node (BSN) 165 may beconfigured to support multicast and broadcast services. The BSN 165 willbe described in greater detail below. The BSN 165 communicates with theRAN 120 (e.g., the BSC/PCF 122) via a broadcast (BC) A10 connection, andwith the application server 170 via the Internet 175. The BCA10connection is used to transfer multicast and/or broadcast messaging.Accordingly, the application server 170 sends unicast messaging to thePDSN 160 via the Internet 175, and sends multicast messaging to the BSN165 via the Internet 175.

Generally, as will be described in greater detail below, the RAN 120transmits multicast messages, received from the BSN 165 via the BCA10connection, over a broadcast channel (BCH) of the air interface 104 toone or more access terminals 200.

Referring to FIG. 3, an access terminal 200, (here a wireless device),such as a cellular telephone, has a platform 202 that can receive andexecute software applications, data and/or commands transmitted from theRAN 120 that may ultimately come from the carrier network 126, theInternet and/or other remote servers and networks. The platform 202 caninclude a transceiver 206 operably coupled to an application specificintegrated circuit (“ASIC” 208), or other processor, microprocessor,logic circuit, or other data processing device. The ASIC 208 or otherprocessor executes the application programming interface (“API”) 210layer that interfaces with any resident programs in the memory 212 ofthe wireless device. The memory 212 can be comprised of read-only orrandom-access memory (RAM and ROM), EEPROM, flash cards, or any memorycommon to computer platforms. The platform 202 also can include a localdatabase 214 that can hold applications not actively used in memory 212.The local database 214 is typically a flash memory cell, but can be anysecondary storage device as known in the art, such as magnetic media,EEPROM, optical media, tape, soft or hard disk, or the like. Theinternal platform 202 components can also be operably coupled toexternal devices such as antenna 222, display 224, push-to-talk button228 and keypad 226 among other components, as is known in the art.

Accordingly, an embodiment can include an access terminal including theability to perform the functions described herein. As will beappreciated by those skilled in the art, the various logic elements canbe embodied in discrete elements, software modules executed on aprocessor or any combination of software and hardware to achieve thefunctionality disclosed herein. For example, ASIC 208, memory 212, API210 and local database 214 may all be used cooperatively to load, storeand execute the various functions disclosed herein and thus the logic toperform these functions may be distributed over various elements.Alternatively, the functionality could be incorporated into one discretecomponent. Therefore, the features of the access terminal in FIG. 3 areto be considered merely illustrative and the embodiments are not limitedto the illustrated features or arrangement.

The wireless communication between the access terminal 102 and the RAN120 can be based on different technologies, such as code divisionmultiple access (CDMA), WCDMA, time division multiple access (TDMA),frequency division multiple access (FDMA), Orthogonal Frequency DivisionMultiplexing (OFDM), the Global System for Mobile Communications (GSM),or other protocols that may be used in a wireless communications networkor a data communications network. The data communication is typicallybetween the client device 102, MPT/BS 124, and BSC/PCF 122. The BSC/PCF122 can be connected to multiple data networks such as the carriernetwork 126, PSTN, the Internet, a virtual private network, and thelike, thus allowing the access terminal 102 access to a broadercommunication network. As discussed in the foregoing and known in theart, voice transmission and/or data can be transmitted to the accessterminals from the RAN using a variety of networks and configurations.Accordingly, the illustrations provided herein are not intended to limitthe embodiments and are merely to aid in the description of aspects ofembodiments.

Below, a description of multicast call-setup for multicast sessions thatare carried on a downlink broadcast channel (BCH) in both target andsupporting sectors will be described, followed by a description ofmulticast call-setup for multicast sessions that are carried in one ormore target sectors (e.g., but not necessarily in supporting sectors).As used herein, a target sector is any sector within a wirelesscommunications system having (or expected to have) at least onemulticast group member that carries a multicast flow for a givenmulticast session, and a supporting sector is any sector within thewireless communications system that is not expected to have multicastgroup members and also carries the multicast flow (e.g., to enable softcombining in target sectors for high-data rate multicastcommunications). Target and supporting sector behavior is discussed inmore detail within Non-Provisional U.S. Provisional Patent ApplicationNo. 60/974,800, entitled “MULTICAST COMMUNICATIONS WITHIN A WIRELESSCOMMUNICATIONS NETWORK”, by Song et al., having attorney docket no.071249P1, filed on Sep. 24, 2007, assigned to the assignee hereof andexpressly incorporated by reference herein in its entirety.

Accordingly, FIG. 4A illustrates a multicast call-setup process for amulticast session to be carried on a downlink BCH in both target andsupporting sectors according to an embodiment. Referring to FIG. 4A, in400, the application server 170 (e.g., a QChat or Push-to-Talk (PTT)server) receives a request to initiate a multicast session (e.g., from aPTT initiator, not shown). In 405, the application server 170 forwardsan announce message to the RAN 120 for transmission to access terminals(“multicast group members”, e.g., ATs 1 . . . N) that belong to amulticast group of the multicast session. For example, the applicationserver 170 can forward the announce message to the RAN 120 through theBSN 165 via a BCA10 connection. In 410, the RAN 120 receives theannounce message over the BCA10 connection and transmits the announcemessage to ATs 1 . . . N over the air interface 104 (e.g., as adata-over-signaling (DOS) message on the downlink CCH, via a standardpaging of ATs 1 . . . N, etc.). ATs 1 . . . N receive the announcemessage and one or more of ATs 1 . . . N register for the multicastsession, 415 (e.g., by transmitting a BCMCSFlowRegistration message) andsend an announce acknowledgment (ACK) that the RAN 120 forwards to theapplication server 170.

Based at least in part on the registrations received from ATs 1 . . . N,the RAN 120 determines the initial target and supporting sectors for themulticast session, 420. FIG. 4B illustrates an example cluster (i.e., aset of target and supporting sectors that carry a flow for the multicastsession, referred to as a ‘multicast flow’, on the sameinterlace-multiplex (IM) pair of a downlink broadcast channel (BCH))that may be formed in 420 of FIG. 4A. As shown, FIG. 4B assumes that ATsA . . . G have registered for the multicast session, that ATs A . . . Greside in target sectors T1 through T4, respectively, and that targetsectors T1 through T4 are supported by supporting sectors S1 throughS12. Cluster origination is described in greater detail within theabove-incorporated co-pending patent entitled “METHODS OF PROVIDINGMULTICAST COMMUNICATIONS WITHIN A WIRELESS COMMUNICATIONS NETWORK”.While one cluster is illustrated in FIG. 4B, it will be appreciated thatmultiple clusters can be formed in the wireless communication system,with each cluster carrying the multicast flow on the same IM pair of thedownlink BCH, or alternatively upon two or more different IM pairs basedon BCH scheduling considerations at the RAN 120.

The RAN 120 transmits a scheduling message (e.g., a broadcast overheadmessage (BOM)) in the target and supporting sectors, 425. For example,the BOM can include an advertisement of the announced multicast session,along with information instructing ATs 1 . . . N on how to tune to themulticast session on the downlink BCH (e.g., an interlace-multiplex (IM)pair on the downlink BCH upon which multicast messages for the multicastsession are to be transmitted). As will be appreciated by one ofordinary skill in the art, the RAN 120 attempts to configure each sectorof the cluster to carry the multicast session on the same IM pair toenhance soft combining (e.g., as used herein, if sectors carry themulticast flow or session on different IM pairs, the sectors will beconstrued as being part of different clusters, and a sector transmittingon multiple IM pairs will be construed as belonging to multipleclusters). In a further example, BOMs transmitted in target sectors areconfigured to suppress subsequent AT registrations (e.g., RFDB=‘0’ toreduce traffic, except for when the RAN 120 wants to confirm the statusof the target sectors), and BOMs transmitted in supporting sectors areconfigured to prompt AT registrations (e.g., so that the RAN 120 cantransition the supporting sector to a target sector, e.g., RFDB=‘1’).Accordingly, the ATs 1 . . . N that have received the BOM tune to theindicated IM pair and monitor for the multicast messages, 430.

In 435, after the application server 170 receives a first announce ACKfor the multicast session, the application server 170 begins forwardingmulticast messages (e.g., multicast media messages, such as video,audio, text, etc.) to the RAN 120 via the BSN 165 over the BCA10connection for transmission to ATs 1 . . . N. In 440, the RAN 120receives the multicast messages over the BCA10 connection and transmitsthe multicast messages to ATs 1 . . . N over the air interface 104 onthe BOM-indicated IM pair of the downlink BCH, in both the target andsupporting sectors. The ATs 1 . . . N that have tuned to theBOM-indicated IM pair of the downlink BCH receive and decode themulticast messages, 445.

As will be appreciated by one of ordinary skill in the art, transmittingmulticast messages in supporting sectors to be used for soft combiningfor access terminals within the target sectors helps the accessterminals decode high-data rate broadcasts or multicasts. However, ifthe multicast has a relatively low-data rate (e.g., a push-to-talk (PTT)call, a VoIP call, etc.), the access terminals may not necessarily needto soft combine with the supporting sector transmission(s) to decode themulticast messages successfully. Also, if multicast group members arenot geographically densely located (e.g., there are not a high number ofmulticast group members in any particular target sector), then thepotentially large number of supporting sectors may decrease an overallspectral efficiency because many sectors are transmitting redundantinformation to reach only a few local multicast group members.

Accordingly, embodiments wherein supporting sectors need not be usedwill now be described in greater detail with respect to FIGS. 5A-8. FIG.5A illustrates a multicast call-setup process for a multicast session tobe carried on the downlink BCH in one or more target sectors accordingto an embodiment. 500 through 515 of FIG. 5A correspond to 400 through415 of FIG. 4A, and as such a further description thereof has beenomitted for the sake of brevity. In 520, the RAN 120 determines whetherto form a cluster upon which to carry the multicast session thatincludes both supporting sectors and target sectors, as in FIG. 4A, orwhether to form the cluster to include only target clusters. Forexample, if the RAN 120 determines the multicast session to be arelatively low data-rate communication, the RAN 120 may determine softcombining to be unnecessary and as such can omit the supporting sectors.If the RAN 120 determines in 520 to include both target and supportingsectors, the process advances to 420 of FIG. 4A. Otherwise, if the RAN120 determines in 520 to include only target sectors, the processadvances to 525 of FIG. 5A.

Referring to FIG. 5A, in 525, based at least in part on theregistrations received from ATs 1 . . . N (in 515), the RAN 120determines a cluster including target sectors, and no supportingsectors, for the multicast session. FIG. 5B illustrates an examplecluster (i.e., a set of target sectors, in this case) that may be formedin 525 of FIG. 5A. As shown, FIG. 5B assumes that ATs A . . . G haveregistered for the multicast session, that ATs A . . . G reside intarget sectors T1 through T4, respectively, and that target sectors T1through T4 do not include supporting sectors (e.g., as compared withFIG. 4B, which includes supporting sectors S1 through S12). In anexample, the determination of 520 may affect a localized set of targetsectors, such that other clusters in other areas of the wirelesscommunications system 100 can include supporting sectors and theno-supporting sector determination affects only a limited set of targetsectors. Alternatively, the determination of 520 may be global, suchthat supporting sectors need not be used throughout the wirelesscommunications system 100. Accordingly, the RAN 120 transmits a BOMwithin the target sectors that lists or advertises a flow identifier(ID) (e.g., a BCMCSFlowID) of the announced multicast session and an IMpair on the BCH that carries the multicast flow, 530, and ATs 1 . . . N(e.g., ATs 1 . . . G in FIG. 5B) tune to the BOM-indicated IM pair onthe downlink BCH, 535, after decoding the BOM. After receiving a firstannounce ACK, the application server 170 begins to forward multicastmessages to the RAN 120, 540, and the RAN 120 receives the multicastmessages over the BCA10 connection and transmits the multicast messagesto ATs 1 . . . N over the air interface 104 on the BOM-indicated IM pairof the downlink BCH, in the targets sectors, 545. The ATs 1 . . . N thathave tuned to the BOM-indicated IM pair of the downlink BCH receive anddecode the multicast messages, 550.

As will be appreciated, while the RAN 120 is illustrated in FIG. 5A asdetermining to form the cluster with or without supporting sectors in520 of FIG. 5A, this determination may alternatively take place at theapplication server 170 in other embodiments, and may then be indicatedto the RAN 120 via a flag (e.g., a DSCP value in a header portion of oneor more multicast packets) or by some other indicia.

As described above, FIG. 5A illustrates how to establish a multicastflow to be carried on target sectors instead of both target andsupporting sectors, such that spectral efficiency savings associatedwith this approach are achieved because fewer sectors transmit the samemulticast messages redundantly. Also, as will be appreciated by one ofordinary skill in the art, omitting supporting sectors reduces thecomplexity of mobility management, because transitions to or fromsupporting-sector states need not be computed when a new multicast groupmember joins a multicast session, departs a multicast session, enters orexits a given sector, etc. However, because the supporting sectors arenot included for transmitting the multicast flow on the same IM pair insectors at least adjacent to the target sectors, the probability that anaccess terminal moving or handing off from a target sector into anon-target sector will miss multicast packets is increased, because agiven delay period is incurred before the access terminal requestsregistration in the non-target sector to prompt the RAN 120 to carry themulticast flow in the new sector.

In conventional multicasting protocols, such as 1x EV-DO, registrationmessages (e.g., BCMCSFlowRegistration Messages) transmitted from accessterminals are defined to be sent on a fixed, periodic slot of thereverse link access channel. Accordingly, upon entering a non-targetsector during an active multicast session, the given delay period startsat an entry time into the non-target sector (e.g., a time of handoff,power-up and/or or a time at which multicast messages transmitted withinthe old target sector can no longer be decoded), plus a waiting time fordetermining the multicast flow is not being carried (e.g., based on anexpiration of a broadcast overhead period without receiving a BOM, basedon receiving a BOM that fails to indicate that the new sector iscarrying the multicast flow, etc.) plus another waiting time until anext, fixed periodic slot on the reverse link access channel upon whichregistrations are scheduled for transmission, after which the accessterminal can tune to the downlink BCH and decode the multicast flow.Embodiments, which will now be described in greater detail, are directedto more quickly triggering a registration transmission at accessterminals within the wireless communications system upon entry into anon-target sector.

In an example, assume that the process of FIG. 5A is executed and thatthe cluster of FIG. 5B is actively carrying the multicast flow on agiven IM pair. In FIG. 5B, T1 to T4 correspond to a group of sectors(e.g., referred to as a “cluster” or “multicast cluster”) that carry themulticast flow on the same IM pair, while it is also possible that otherclusters (not shown) carry the multicast flow on a different IM pair.With these assumptions, after 550 of FIG. 5A, the process advances to600 of FIG. 6A. FIG. 6A illustrates BCH setup in a non-target sector X1for an active multicast session according to an embodiment. Referring toFIG. 6A, in 600, assume AT G is located at Position 1 within targetsector T4, as illustrated in FIG. 6B. Next, in 605, AT G moves towards aneighboring sector X1, which is a non-target sector, and crosses ahandoff boundary between T4 and X1, and is at Position 2 of FIG. 6B.Accordingly, AT G hands off from T4 to X1. In the handoff zone, AT Greceives transmissions from one or more base stations in one or moresectors carrying the multicast session. For example, if the BOMtransmitted in T4 before the handoff indicates that T4 and T3 arecarrying the multicast flow on the same IM pair, AT G receives themulticast flow from T4, and at least potentially can also receive themulticast flow from T3, which can be used for soft-combining. Withregard to the control channel, if the system 100 is operating inaccordance with DO protocols, soft handoff is not supported, except forthe soft-combining related to the downlink BCH, such that AT G onlymonitors the control channel in its current serving sector. Thus, BOMs(if any) are received at AT G in T4 before the handoff, and BOMs arereceived (if any) in X1 after the handoff. Thus, AT G continues tomonitor the multicast session after the handoff from T4 to X1 based onthe BOM received in T4 from before the handoff, 610, if possible.

In 615, the RAN 120 transmits a scheduling message on the controlchannel within sector X1. In an example, the scheduling message can be aBOM that lists multicast flows being carried on the downlink BCH withinX1. For convenience of explanation, the scheduling message willhereinafter be described as a BOM. However, in other multicastingprotocols, it will be appreciated that embodiments can be directed toany scheduling message that indicates multicast flow status for one ormore sectors. Because AT G has handed off to X1, AT G monitorstransmissions within X1 and as such receives and decodes the BOM, 620.In an example, assume that the BOM received in 615 at AT G is the firstBOM following AT G's entry into the handoff zone between T4 and X1. AT Gevaluates the decoded BOM and determines, 625, either that X1 is notcarrying the desired multicast flow (e.g., if X1's BOM does not list aBCMCSFlowID and associated BCH IM pair), or that X1 is carrying thedesired multicast flow on a different IM pair than sector T4 (e.g., ifX1 corresponds to a different cluster for the multicast flow than thecluster illustrated in FIG. 5B). If AT G determines that X1 is notcarrying the multicast flow, the process advances to 630. Otherwise, ifAT G determines that X1 is carrying the flow on a different IM pair, theprocess advances to 645 and AT G tunes to the indicated IM pair.

As noted above with respect to 610, because AT G's location at Position2 of FIG. 6B is within the service boundary of T4, while AT G is settingup the BCH for the multicast session in X1, AT G continues to monitorthe multicast session based at least in part on transmissions from T4and/or other sectors via soft combining of the downlink BCH, based onBCH-transmissions of neighboring-sectors that also carry the multicastflow on the same BCH IM pair as indicated by the previous BOM in T4received at 545).

The monitoring that begins in 610 is performed at least until a new BOMis decoded for AT G's new sector (e.g., in 645), and can be based on theBOM received in T4 at 545. For example, BOMs may include a list oradvertisement of multicast flows carried in neighboring sectors inaddition to the local sector transmitting the BOM. Thus, if the BOMtransmitted in 545 indicates that neighboring sectors (e.g., T3, etc.)are carrying the multicast flow, AT G soft combines the transmissionsfrom the listed neighboring sector(s) (if possible), carrying themulticast flow, as well as T4's BCH transmissions of the multicast flow,at least until a BOM is received that indicates the new sector iscarrying the multicast flow on the IM pair being decoded by AT G. Whilenot illustrated explicitly within FIG. 6A, it is appreciated that if ATG reaches a point at which AT G cannot decode multicast packetsassociated with the monitored multicast flow, the application layercannot sufficiently correct errors in the multicast flow and/or thepacket error rate reaches an unacceptable level, AT G stops monitoringthe flow. Thus, FIG. 6A assumes that the decoding of the flow at AT G issufficient until AT G's new sector begins to carry the flow itself.

Likewise, while not the case in the present example illustrated in FIG.6B, if X1 is already carrying the multicast flow on the downlink BCH, X1would be a target sector and may be listed in the BOM received from T4on T4's downlink control channel before the handoff to X1. Thus, in anembodiment where AT G hands off from one target sector to another targetsector within the same multicast cluster, AT G need not wait to receivea BOM in its new serving sector following the handoff before decodingthe downlink BCH if a BOM from its old sector already indicates that thenew sector is carrying the multicast flow on the downlink BCH. Thus,although AT G would not yet have the updated list of neighboring sectorsfor the new sector that carry the multicast flow to use insoft-combining, AT G would at least be able to use its new sector's owntransmissions of the multicast flow to soft-combine and perform betterdecoding prior to receipt of the BOM. Thus, in this case, after handingoff from T4 to X1 in 605, AT G can begin decoding multicast messages onthe downlink BCH in X1 before the BOM is decoded at 615. Again, thisscenario is based on the assumption that AT G is handed off betweentarget sectors within a multicast cluster that both carry the samemulticast flow on the same IM pair, and is described in more detailbelow with respect to FIGS. 9A, 9B and 9C.

Also, even though supporting sectors are not included for soft combiningin this example, AT G can soft combine with neighboring target sectors(e.g., listed in the BOM from T4 received at 545 of FIG. 5A) even when aserving target sector is carrying the multicast flow, so long as themulticast flows from the neighbor target sectors remain in range of ATG.

After determining the desired multicast flow is not being carried in X1,AT G transmits an “immediate” registration message (e.g., aBCMCSFlowRegistration message) in X1 to the RAN 120 on the reverse linkaccess channel, 630. As used herein, an “immediate” transmissioncorresponds to a transmission that is earlier than a predefined,periodic slot that is allocated for registration transmissions. Forexample, if slot #7 is the predefined, periodic slot forBCMCSFlowRegistration messages, then any of slots #1-#7 may be“immediate” as used herein. For example, the immediateBCMCSFlowRegistration message transmission can occur on a next availableslot on the reverse link access channel subsequent to the determinationof 620. It is also assumed herein that the RAN 120 is configured todecode the immediate registration message. For example, the RAN 120 canbe configured to decode all slots on the reverse link access channel, oralternatively can be configured to decode only the most likely slotswhere reverse link registration messages are expected, etc. It will beappreciated that there are many different ways in which the RAN 120 canbe implemented to ensure receipt of the immediate registration messagesdescribed herein.

Upon receiving the registration request in X1, the RAN 120 transitionsX1 to target sector T5, and transitions T4 to a non-target sector, 635(e.g., because no multicast group members remain in old target sectorT4), which means the RAN 120 begins to carry the multicast flow in T5and ceases to support the multicast flow in T4. It will be appreciatedthat the transition of T4 to a non-target sector occurs because AT G isthe only multicast group member in T4 in the cluster illustrated in FIG.5B, and AT G then exits the sector T4 and enters sector X1. It will beappreciated that if any multicast group members were to remain in T4(e.g., if AT D or E were to enter T4 before AT G exited, or a newmulticast group member registered to the multicast session in T4), T4would remain a target sector. Also, the transition of T4 to a non-targetsector may be configured to occur at some point after the RAN 120 sendsa BOM in T5 (e.g., in 640), so that AT G does not experience a serviceoutage before AT G can tune to the multicast flow in T5. In an example,FIG. 6C illustrates an updated cluster after the transitioning of 635,based on an initial cluster as illustrated in FIG. 5B. The RAN 120transmits a new scheduling message or BOM that advertises the multicastflow in X1 (now T5), 640, and AT G receives the scheduling message andtunes to the BOM-indicated IM pair on the downlink BCH, 645. It will beappreciated that the RAN 120, if possible, can transmit the multicastflow in X1 (now T5) on the same IM-pair as in any neighboring targetsector(s) of the multicast cluster, such that AT G can attempt tosoft-combine with multicast transmissions on the downlink BCH in anyneighbor target sector as well (e.g., such as T3 if T3 were a neighborsector of T5, etc.). Also, while not shown explicitly in FIG. 6A, uponreceiving the BOM in AT G's new sector (i.e., T5), AT G can update itslist of local sectors that are known to carry the multicast flow, whichnow includes T5 and can include one or more other sectors to be used insoft-combining with T5's multicast flow transmissions. The RAN 120begins to transmit multicast messages on the BOM-indicated IM pair ofthe downlink BCH in X1 (now T5), 650, and AT G monitors the multicastmessages, 655.

As will be appreciated by one of ordinary skill in the art, because AT Gtransmits the registration message (e.g., a BCMCSFlowRegistrationmessage) before the fixed, periodic slot reserved for registrationmessages, the RAN 120 is informed of the presence of a multicast groupmember in X1 more quickly, such that the multicast flow can be carriedIn X1 sooner, which reduces the probability that AT G will drop thecall. Also, T4 transitions to a non-target sector more quickly, whichmeans that transmissions in T4 cease sooner, which improves a spectralefficiency of the wireless communications system 100.

In another example, again assume that the process of FIG. 5A is executedand that the cluster of FIG. 5B is actively carrying the multicast flowon a given IM pair. As noted above, in FIG. 5B, T1 to T4 correspond to agroup of sectors (e.g., referred to as a “cluster” or “multicastcluster”) that carry the multicast flow on the same IM pair, while it isalso possible that other clusters (not shown) carry the multicast flowon a different IM pair. With these assumptions, after 550 of FIG. 5A,the process advances to 700 of FIG. 7. FIG. 7 illustrates BCH setup in anon-target sector X1 for an active multicast session according toanother embodiment. Referring to FIG. 7, in 700, assume AT G is locatedat Position 1 within target sector T4, as illustrated in FIG. 6B. Next,in 705, the RAN 120 transmits a periodic scheduling message (e.g., aBOM) within T4 that advertises the multicast flow and indicates the IMpair carrying the multicast flow in T4 and any neighboring sectors(e.g., T3). As noted above, if AT G operates in a protocol (e.g., DO)where the control channel is not soft-combined, then the decoding of theperiodic scheduling message (e.g., BOM) in 705 occurs prior to thehandoff from T4 to X1 in 710. Again, for convenience of explanation, thescheduling message will hereinafter be described as a BOM. However, inother multicasting protocols, it will be appreciated that embodimentscan be directed to any scheduling message that indicates multicast flowstatus for one or more sectors.

In 710, AT G moves towards a neighboring sector X1, which is anon-target sector, and crosses a handoff boundary between T4 and X1, andis at Position 2 of FIG. 6B. Accordingly, AT G hands off from sector T4to X1. In the handoff zone, AT G receives transmissions from one or morebase stations in one or more sectors carrying the multicast session. Forexample, if the BOM transmitted in T4 before the handoff indicates thatT4 and T3 are carrying the multicast flow on the same IM pair, AT Greceives the multicast flow from T4, and at least potentially can alsoreceive the multicast flow from T3, which can be used for soft-combiningWith regard to the control channel, if the system 100 is operating inaccordance with DO protocols, soft handoff is not supported, except forthe soft-combining related to the downlink BCH, such that AT G onlymonitors the control channel in its current serving sector. Thus, BOMs(if any) are received at AT G in T4 before the handoff, and BOMs arereceived (if any) in X1 after the handoff.

After handing off from T4 to X1, AT G resets a BOM timer, 710. In anexample, the BOM timer has a period equal to a BroadcastOverheadPeriod(e.g., an expected period between BOM transmissions).

Because AT G is within the handoff zone, AT G monitors transmissionsfrom both T4 and X1. In 720, AT G continues to monitor the multicastsession based at least in part on transmissions from T4 and/or othersectors via soft combining of the downlink BCH, (e.g., such asBCH-transmissions of neighboring-sectors that also carry the multicastflow on the same BCH IM pair as indicated by the previous BOM in T4received at 705). The monitoring that occurs in 720 is performed atleast until a new BOM is decoded for AT G's new sector (e.g., in 750),and can be based on the BOM received in T4 at 705. For example, BOMs mayinclude a list or advertisement of multicast flows carried inneighboring sectors in addition to the local sector. Thus, if the BOMtransmitted in 705 indicates that neighboring sectors (e.g., T3, etc.)are carrying the multicast flow, AT G soft combines the transmissionsfrom those neighboring sectors (if possible) as well as T4, at leastuntil a BOM is received that indicates the new sector X1 is carrying themulticast flow. However, while not illustrated explicitly within FIG. 7,it is appreciated that if AT G reaches a point at which AT G cannotdecode multicast packets associated with the monitored multicast flow,the application layer cannot sufficiently correct errors in themulticast flow and/or the packet error rate reaches an unacceptablelevel, AT G stops monitoring the flow. Thus, FIG. 7 assumes that thedecoding of the flow via soft-combining at AT G is sufficient until ATG's new sector begins to carry the flow itself.

In 725, AT G determines whether a BOM has been received in sector X1that advertises the multicast flow (e.g., either on the same IM pair asin T4 that is currently being decoded by AT G, or on a different IMpair). If a BOM has been received that advertises the multicast flow,the process advances to 750, and AT G tunes to the IM pair advertises assupporting the multicast flow (e.g., either on the same IM pair as in T4that is currently being decoded by AT G, or on a different IM pair).While not shown in FIG. 7, if a BOM is received that does not advertisethe multicast flow, the process advances to 620 of FIG. 6A. Otherwise,if no BOM has been received in sector X1, the process advances to 730.In 730, AT G determines whether the BOM timer is expired. If the BOMtimer is not expired, the process returns to 720, AT G continues tosoft-combine transmissions of the multicast flow from one or more othersectors and waits to receive a BOM in sector X2. Otherwise, if the BOMtimer is expired, AT G transmits an immediate registration message forthe multicast session, 735, as in 630 of FIG. 6A. As discussed above, an“immediate” transmission corresponds to a transmission that is earlierthan a predefined, periodic slot that is allocated for registrationtransmissions based on the wireless multicasting protocol (e.g., 1xEV-DO). 740 through 760 of FIG. 7 correspond to 635 to 655 of FIG. 6A,respectively, which have already been described above. Accordingly, afurther description thereof has been omitted for the sake of brevity.

In yet another example, again assume that the process of FIG. 5A isexecuted and that the cluster of FIG. 5B is actively carrying themulticast flow on a given IM pair. As noted above, in FIG. 5B, T1 to T4correspond to a group of sectors (e.g., referred to as a “cluster” or“multicast cluster”) that carry the multicast flow on the same IM pair,while it is also possible that other clusters (not shown) carry themulticast flow on a different IM pair. With these assumptions, after 550of FIG. 5A, the process advances to 800 of FIG. 8. FIG. 8 illustratesBCH setup in a non-target sector X1 for an active multicast sessionaccording to yet another embodiment. Referring to FIG. 8, in 800, assumeAT G is located at Position 1 within target sector T4, as illustrated inFIG. 6B. Next, in 805, the RAN 120 transmits a periodic schedulingmessage (e.g., a BOM) within T4 that advertises the multicast flowwithin T4 and indicates the IM pair carrying the multicast flow in T4and any neighboring sectors (e.g., T3). Within this example, assume thatthe BOM of 805 indicates either that the multicast session is not beingcarried in X1 or that the multicast session is not being carried in X1on the same IM pair as T4. For example, the indication that themulticast session is not carried in X1 can be achieved by configuringthe BOM to in T4 to list the neighboring sectors of T4 that carry themulticast flow on the same IM pair as T4, and to omit X1 from this list.It will be appreciated that the failure of the T4 BOM to indicate X1 inthis manner indicates either that the multicast flow is not beingcarried in X1 at all, or is being carried on a different IM pair.

In 810, AT G moves towards the neighboring sector X1, which is anon-target sector, and crosses a handoff boundary between T4 and X1,hands off from T4 to X1, and is at Position 2 of FIG. 6B. In the handoffzone, AT G receives transmissions on the downlink BCH from one or morebase stations in one or more sectors carrying the multicast session(e.g., from the base station serving sector T4 so long as T4 remains atarget sector, from the base station serving sector X1 if X1 is carryingthe multicast flow on the given IM pair as indicated by a BOM from T4 in805, from one or more neighboring sectors of T4 that carry the multicastflow on the given IM pair as indicated by the BOM from 805, etc.). In815, AT G continues to monitor the multicast session based at least inpart on transmissions from T4, and/or other sectors via soft combining,as described above. The monitoring that occurs in 815 is performed atleast until a new BOM is decoded for AT G's new sector (e.g., in 840),and can be based on sectors indicating to be carrying the multicast flowon the given IM pair as determined from the BOM received in T4 at 805.However, while not illustrated explicitly within FIG. 8, it isappreciated that if AT G reaches a point at which AT G cannot decodemulticast packets associated with the monitored multicast flow, theapplication layer cannot sufficiently correct errors in the multicastflow and/or the packet error rate reaches an unacceptable level, AT Gstops monitoring the flow. Thus, FIG. 8 assumes that the decoding of theflow via soft-combining at AT G is sufficient until AT G's new sectorbegins to carry the flow itself.

In 820, upon entry into the handoff zone at Position 2 and handing offto X1, AT G determines that sector X1 either does not carry themulticast flow at all or does not carry the multicast flow on the samegiven IM pair based on the previously received BOM in T4. As will beappreciated, the determination of 820 in this embodiment is based on aprevious BOM received in AT G's old sector T4, and not based on anactual BOM yet received in sector X1. Thus, AT G need not wait toreceive a BOM in X1 (e.g., as in FIG. 6A) or an expiration of a BOMtimer (e.g., as in FIG. 7) to learn that X1 does not carry the multicastflow. Accordingly, AT G transmits an immediate registration to the RAN120 in sector X1 subsequent to the handoff in 825, with “immediate”being defined above with respect to 630 of FIG. 6A and 735 of FIG. 7.Next, 830 through 850 of FIG. 8 correspond to 635 to 655 of FIG. 6A,respectively, which have already been described above. Accordingly, afurther description thereof has been omitted for the sake of brevity.

Also, while not shown explicitly in FIG. 8, if AT G determines in 820that X1 is carrying the multicast flow on a different IM pair than T4,AT G can advance directly to 840 and tune to the different IM pair.Thus, in this case, a registration message need not be sent to promptthe RAN 120 to carry the multicast flow, and AT G can simply tune to themulticast flow on the IM pair that is supporting the flow in the nextsector.

As will be appreciated by one of ordinary skill in the art, each of theembodiments illustrated in FIGS. 6A, 7 and 8, respectively, are directedto establishing a multicast flow on a downlink BCH in a non-targetsector to which one or more multicast group members migrate during anactive multicast session. Instead of waiting for the fixed, periodicslot on which to send registration messages, each of the embodimentsillustrated in FIGS. 6A, 7 and 8, respectively, teach different mannersby which a non-target status of a newly entered sector can be inferredby an access terminal, thereby triggering a transmission of theregistration message that is potentially earlier than the fixed,periodic slot.

Further, while described as separate embodiments, each of theembodiments described with respect to FIGS. 6A, 7 and 8 can be usedseparately or together. For example, a BOM timer can be reset and usedto determine the presence of a multicast flow as in FIG. 7, while BOMsreceived in the new sector are evaluated as in FIG. 6A.

Further, while FIGS. 6A, 7 and 8 have been directed to embodimentswherein no supporting sectors are included in a multicast cluster, itwill be appreciated that the embodiments described above are applicableto any multicast transmission scenario where the multicast flow iscarried on a downlink BCH and a multicast group member handoffs from atarget sector to a sector that is not carrying the multicast flow. Thus,even if supporting sectors are present in other portions of the clusterfor supporting other target sectors (e.g., such as target sectors withespecially poor channel conditions, etc.), the embodiments describedabove can still be implemented where a supporting sector is not present.In this case, the supporting sectors could be used for soft-combiningthe multicast flow on the downlink BCH, as described above with respectto target sectors. In other words, a BOM in a previous or current sectorcan advertise a supporting sector carrying the multicast flow on a givenIM pair, for which the AT can use to soft-combine the flow, irrespectiveof whether the advertised sector is a supporting sector or a targetsector.

While embodiments described above are directed to sending immediateregistrations for a multicast flow or session when an AT migrates from atarget sector to a non-target sector, other embodiments can be directedto when an AT migrates from a target sector to another target sector, aswill now be described with respect to FIGS. 9A through 9C.

As in FIGS. 6A, 7 and 8, again assume that the process of FIG. 5A isexecuted and that the cluster of FIG. 5B is actively carrying themulticast flow on a given IM pair. As noted above, in FIG. 5B, T1 to T4correspond to a group of sectors (e.g., referred to as a “cluster” or“multicast cluster”) that carry the multicast flow on the same IM pair,while it is also possible that other clusters (not shown) carry themulticast flow on a different IM pair. With these assumptions, after 550of FIG. 5A, the process advances to 900 of FIG. 9A. FIG. 9 illustratesBCH setup for an AT (“AT G”) that migrates from a current target sectorT4 to an adjacent target sector T3 according to yet another embodiment.Referring to FIG. 9A, in 900, assume AT G is located at Position 1within target sector T4, as illustrated in FIG. 9B. Next, in 905, theRAN 120 transmits a periodic scheduling message (e.g., a BOM) within T4that advertises the multicast flow within T4 and indicates the IM paircarrying the multicast flow in T4 and any neighboring sectors (e.g.,T3). Within this example, assume that the BOM of 905 indicates that themulticast session is being carried at least within sectors T4 and T3 onthe same IM pair.

In 910, AT G moves towards the target sector T3, crosses a handoffboundary between T4 and T3, hands off from T4 to T3, and is at Position2 of FIG. 9B. In the handoff zone, AT G receives transmissions on thedownlink BCH on the monitored IM pair from both the base station servingsector T4 (e.g., for so long as T4 remains a target sector), and fromthe base station serving sector T3 because T3 is carrying the multicastflow on the given IM pair as indicated by a BOM from T4 in 905, and/orfrom one or more other neighboring sectors of T4 that carry themulticast flow on the given IM pair as indicated by the BOM from 905.

In 915, upon entry into the handoff zone at Position 2 and handing offto T3, AT G determines that sector T3 is carrying the multicast flow onthe same IM pair that is already being monitored by AT G based on theprevious BOM that is received in target sector T4 before the handoff of910. Thus, as will be appreciated, the determination of 915 in thisembodiment is based on a previous BOM received in AT G's old sector T4,and not based on an actual BOM yet received AT G's new sector T3. Thus,AT G need not wait to receive a BOM in T3 or an expiration of a BOMtimer to learn that T3 is already carrying the multicast flow on thegiven IM pair. Accordingly, AT G tunes (or continues to tune) to the IMpair of the downlink BCH in target sector T3, and if possible can softcombine with one or more other sectors (e.g., such as T4) to increasethe decode success rate, 920. For example, AT G can soft combine withmulticast flow transmissions on the downlink BCH of the given IM pairfrom target sector T4 (e.g., until these transmissions terminate in930), as well as potentially one or more neighboring sectors that areindicated in the BOM received T4 at 905 that are also indicated ascarrying the multicast flow at the given IM pair.

Because AT G is already aware that T3 is a target sector (i.e., from theBOM in T4 at 905), AT G may refrain from sending an immediateregistration for the multicast flow in T3, 925. Thus, unlike FIGS. 6A, 7and 8, wherein AT G infers a new sector to be a non-target sector andsends a preemptive or more immediate registration message (e.g.,BCMCSFlowRegistration message), in 925 of FIG. 9, the oppositeconclusion is reached by AT G such that no registration message need besent. However, while not shown in FIG. 9A, AT G may start a timer, whichmay or may not have the same duration as the BOM timer from FIG. 7, andmay send a registration if the timer expires. Thus, if the BOM in T4indicates that T3 is carrying the multicast flow, but T3 has sincestopped carrying the multicast flow, AT G can still obtain the multicastflow in T3 despite T4's BOM from 905 acting as a ‘false-positive’ oftarget sector-status for AT G's new sector in this case.

Turning to the RAN 120, after handing off AT G from target sector T4 totarget sector T3, the RAN 120 maintains target sector T3 as a targetsector, and transitions T4 to a non-target sector, 930 (e.g., because nomulticast group members remain in old target sector T4). It will beappreciated that the transition of T4 to a non-target sector occursbecause AT G is the only multicast group member in T4 in the clusterillustrated in FIG. 9B, and AT G then exits the sector T4 and enterssector T3. It will be appreciated that if any multicast group memberswere to remain in T4 (e.g., if AT D or E were to enter T4 before AT Gexited, or a new multicast group member registered to the multicastsession in T4), T4 would remain a target sector. In an example, FIG. 9Cillustrates an updated cluster after the transitioning of 930, based onan initial cluster as illustrated in FIG. 5B.

The RAN 120 transmits a new scheduling message or BOM that advertisesthe multicast flow in target sector T3 as well as any neighboringsectors that carry the multicast flow on a given IM pair, 935, and AT Greceives the scheduling message and updates its list of local sectorsthat are known to carry the multicast flow, 940. For example, theupdated list continues to include target sector T3, which was alsolisted in the BOM in T4 at 905. The updated list now omits target sectorT4 because T4 has transitioned to a non-target sector. The updated listmay potentially include other neighboring sectors carrying the multicastflow as well, such as T1 and/or T2. It will be appreciated that due toscheduling on the BCH, it may not always be possible for the RAN 120 toschedule the multicast flow in T3 on the same IM pair as in T4. Thus, itis possible that the BOM sent in T3, 935, may advertise the multicastflow on a different IM pair than in T4.

In 945, AT G continues to tune to the BOM-indicated IM pair on thedownlink BCH in T3, and also soft-combines with other sectors indicatedas carrying the multicast flow in the BOM of 935, if possible, 945. Itwill be appreciated that the RAN 120, if possible, can transmit themulticast flow in T3 on the same IM-pair as in any neighboring targetsector(s) of the multicast cluster, such that AT G can attempt tosoft-combine with multicast transmissions on the downlink BCH in anyneighbor target sector as well (e.g., such as T2 if T2 were a neighborsector of T3, etc.). Also, if the BOM of 935 advertises the multicastflow on a different IM pair than the previous IM pair from the BOM of905, then AT G switches to the new IM pair. If this occurs, softcombining with the ‘old’ IM pair is not necessarily possible, althoughAT G may be able to soft combine with other sectors that also transmitthe multicast flow on the new IM pair indicated in 935.

The RAN 120 continues to transmit multicast messages on theBOM-indicated IM pair of the downlink BCH in T3 (e.g., and potentiallyone or more other sectors for use in soft-combining at AT G), 950, andAT G monitors the multicast messages, 955.

Accordingly, in the embodiment of FIG. 9A, it will be appreciated thatthe level of traffic on the reverse link access channel is reduced dueto AT G refraining from sending a registration message in 925 (i.e.,because AT G's new sector was already a target sector carrying themulticast flow on the same IM pair as AT G's old sector). Also, becauseAT G was aware as soon as handoff occurred in 910 that AT G's new sectorwas a target sector (i.e., 915), AT G began decoding the downlink BCHfor the multicast flow in T3 more quickly (i.e., at 920 of FIG. 9A) thanif AT G had waited for a next BOM in the target sector T3 in 950 (i.e.,after 935 of FIG. 9A).

Accordingly, as will be appreciated by one of ordinary skill in the artin view of the embodiments described above, when a given AT monitoring amulticast session hands off to a new sector, the given AT determineswhether the new sector is already supporting the multicast session onthe same IM pair as the given AT's old sector based on (i) a BOMreceived in the new sector (e.g., FIG. 6A), (ii) a BOM received in theold sector (e.g., see FIG. 8 and/or FIG. 9A), and/or (iii) by a BOMtimer expiring before a BOM in the new sector is received (e.g., seeFIG. 7), and/or any combination of (i), (ii) or (iii). If the new sectoris determined to already be supporting the multicast flow on the same IMpair as the old sector, the given AT may refrain from sending aregistration message (e.g., see FIG. 9A). Otherwise, if the new sectoris determined not to be supporting the multicast flow on the same IMpair as the old sector based on (i), (ii) and/or (iii), an “immediate”registration message can be sent from the given AT to the RAN 120 in thenew sector (e.g., see 630 of FIG. 6A, 735 of FIG. 7 and/or 825 of FIG.8), which can prompt the new sector to carry the multicast flow morequickly. Also, while the given AT waits for the new sector to carry themulticast flow, the given AT can monitor the downlink BCH transmissionfor the multicast flow on the given IM pair for one or more sectorsbased on a BOM received in the given AT's old sector before the handoff(e.g., see 625 of FIG. 6A, 720 of FIG. 7 and/or 815 of FIG. 8), suchthat the probability of the given AT dropping the multicast flow beforeit is carried in the new sector is reduced.

Further, a ‘non-target sector’ as described above has been describedrelative to a particular multicast flow. Thus, in embodiments describedabove, a sector qualifies a non-target sector if the sector does notcarry a particular multicast flow. However, it will be appreciated thatthis may mean that the non-target sector does not carry any multicastflows in certain embodiments, while this may alternatively mean that thenon-target sector carries at least one multicast flow, but not themulticast flow relevant to the particular embodiment being discussed.Thus, a non-target sector may carry one or more multicast flows formulticast sessions other than the multicast session at issue.

Those of skill in the art will appreciate that information and signalsmay be represented using any of a variety of different technologies andtechniques. For example, data, instructions, commands, information,signals, bits, symbols, and chips that may be referenced throughout theabove description may be represented by voltages, currents,electromagnetic waves, magnetic fields or particles, optical fields orparticles, or any combination thereof.

Further, those of skill in the art will appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the embodiments.

The various illustrative logical blocks, modules, and circuits describedin connection with the embodiments disclosed herein may be implementedor performed with a general purpose processor, a digital signalprocessor (DSP), an application specific integrated circuit (ASIC), afield programmable gate array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The methods, sequences and/or algorithms described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such that theprocessor can read information from, and write information to, thestorage medium. In the alternative, the storage medium may be integralto the processor. The processor and the storage medium may reside in anASIC. The ASIC may reside in a user terminal (e.g., access terminal). Inthe alternative, the processor and the storage medium may reside asdiscrete components in a user terminal

In one or more exemplary embodiments, the functions described may beimplemented in hardware, software, firmware, or any combination thereof.If implemented in software, the functions may be stored on ortransmitted over as one or more instructions or code on acomputer-readable medium. Computer-readable media includes both computerstorage media and communication media including any medium thatfacilitates transfer of a computer program from one place to another. Astorage media may be any available media that can be accessed by acomputer. By way of example, and not limitation, such computer-readablemedia can comprise RAM, ROM, EEPROM, CD-ROM or other optical diskstorage, magnetic disk storage or other magnetic storage devices, or anyother medium that can be used to carry or store desired program code inthe form of instructions or data structures and that can be accessed bya computer. Also, any connection is properly termed a computer-readablemedium. For example, if the software is transmitted from a website,server, or other remote source using a coaxial cable, fiber optic cable,twisted pair, digital subscriber line (DSL), or wireless technologiessuch as infrared, radio, and microwave, then the coaxial cable, fiberoptic cable, twisted pair, DSL, or wireless technologies such asinfrared, radio, and microwave are included in the definition of medium.Disk and disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu-ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer-readable media.

While the foregoing disclosure shows illustrative embodiments of thedisclosure, it should be noted that various changes and modificationscould be made herein without departing from the scope of the embodimentsas defined by the appended claims. The functions, steps and/or actionsof the method claims in accordance with the embodiments described hereinneed not be performed in any particular order. Furthermore, althoughelements of the embodiments may be described or claimed in the singular,the plural is contemplated unless limitation to the singular isexplicitly stated.

1. A method of multicasting within a wireless communications systemoperating in accordance with a given wireless communication protocol,comprising: monitoring multicast messages associated with a givenmulticast session in a first sector; receiving a first schedulingmessage within the first sector that advertises the given multicastsession as carried in the first sector and at least a second sector, andfurther indicates how an access terminal can tune to the given multicastsession in the first and second sectors; handing off from the firstsector to the second sector; determining, based on the first schedulingmessage, that the second sector is carrying the given multicast session;refraining from transmitting a registration request for the givenmulticast session within the second sector based on the first schedulingmessage; and attempting to monitor multicast messages associated withthe given multicast session in the second sector.
 2. The method of claim1, further comprising: receiving a second scheduling message within thesecond sector that advertises the given multicast session as carried inthe second sector, and further indicates how an access terminal can tuneto the given multicast session in the second.
 3. The method of claim 2,wherein the second scheduling message indicates at least one otherneighboring target sector that is carrying the given multicast sessionon the same Interlace-Multiplex (IM) pair as the second sector.
 4. Themethod of claim 3, further comprising: establishing an initial list ofsectors known to be carrying the given multicast session based on thefirst scheduling message; updating, at the access terminal, the initiallist of sectors known to be carrying the given multicast session basedon the second scheduling message, wherein, after the updating, theattempting includes attempting to soft combine multicast messagesassociated with the given multicast message that are received from thesecond sector and the at least one neighboring target sector.
 5. Themethod of claim 1, wherein the attempting continues until (i) the accessterminal cannot decode multicast packets associated with the givenmulticast session, an application layer cannot sufficiently correcterrors in the given multicast session or a packet error rate reaches anunacceptable level, or (ii) a second scheduling message is receivedwithin the second sector that advertises the given multicast session ascarried in the second sector, and further indicates how an accessterminal can tune to the given multicast session in the second sector.6. The method of claim 1, wherein the first scheduling messagecorresponds to a broadcast overhead message (BOM).
 7. A non-transitorycomputer-readable storage medium comprising instructions, which, whenexecuted by at least one processor provide for multicasting within awireless communications system operating in accordance with a givenwireless communication protocol, the instructions comprising:instructions to monitor multicast messages associated with a givenmulticast session in a first sector; instructions to receive a firstscheduling message within the first sector that advertises the givenmulticast session as carried in the first sector and at least a secondsector, and further indicates how an access terminal can tune to thegiven multicast session in the first and second sectors; instructions tohand off from the first sector to the second sector; instructions todetermine, based on the first scheduling message, that the second sectoris carrying the given multicast session; instructions to refrain fromtransmitting a registration request for the given multicast sessionwithin the second sector based on the first scheduling message; andinstructions to attempt to monitor multicast messages associated withthe given multicast session in the second sector.
 8. An apparatusconfigured for multicasting within a wireless communications systemoperating in accordance with a given wireless communication protocol,the apparatus comprising: logic configured to monitor multicast messagesassociated with a given multicast session in a first sector; logicconfigured to receive a first scheduling message within the first sectorthat advertises the given multicast session as carried in the firstsector and at least a second sector, and further indicates how an accessterminal can tune to the given multicast session in the first and secondsectors; logic configured to hand off from the first sector to thesecond sector; logic configured to determine, based on the firstscheduling message, that the second sector is carrying the givenmulticast session; logic configured to refrain from transmitting aregistration request for the given multicast session within the secondsector based on the first scheduling message; and logic configured toattempt to monitor multicast messages associated with the givenmulticast session in the second sector.
 9. The non-transitorycomputer-readable storage medium of claim 7, further comprising:instructions to receive a second scheduling message within the secondsector that advertises the given multicast session as carried in thesecond sector, and further indicates how an access terminal can tune tothe given multicast session in the second.
 10. The non-transitorycomputer-readable storage medium of claim 9, wherein the secondscheduling message indicates at least one other neighboring targetsector that is carrying the given multicast session on the sameInterlace-Multiplex (IM) pair as the second sector.
 11. Thenon-transitory computer-readable storage medium of claim 10, furthercomprising: instructions to establish an initial list of sectors knownto be carrying the given multicast session based on the first schedulingmessage; instructions to update, at the access terminal, the initiallist of sectors known to be carrying the given multicast session basedon the second scheduling message, wherein, after the initial list ofsectors is updated by the instructions to update, the instructions toattempt attempts to soft combine multicast messages associated with thegiven multicast message that are received from the second sector and theat least one neighboring target sector.
 12. The non-transitorycomputer-readable storage medium to of claim 7, wherein the instructionsto attempt continue attempting to monitor until (i) the access terminalcannot decode multicast packets associated with the given multicastsession, an application layer cannot sufficiently correct errors in thegiven multicast session or a packet error rate reaches an unacceptablelevel, or (ii) a second scheduling message is received within the secondsector that advertises the given multicast session as carried in thesecond sector, and further indicates how an access terminal can tune tothe given multicast session in the second sector.
 13. The non-transitorycomputer-readable storage medium of claim 7, wherein the firstscheduling message corresponds to a broadcast overhead message (BOM).14. The apparatus of claim 8, further comprising: logic configured toreceive a second scheduling message within the second sector thatadvertises the given multicast session as carried in the second sector,and further indicates how an access terminal can tune to the givenmulticast session in the second.
 15. The apparatus of claim 14, whereinthe second scheduling message indicates at least one other neighboringtarget sector that is carrying the given multicast session on the sameInterlace-Multiplex (IM) pair as the second sector.
 16. The apparatus ofclaim 15, further comprising: logic configured to establish an initiallist of sectors known to be carrying the given multicast session basedon the first scheduling message; logic configured to update, at theaccess terminal, the initial list of sectors known to be carrying thegiven multicast session based on the second scheduling message, wherein,after the initial list of sectors is updated by the logic configured toupdate, the logic configured to attempt attempts to soft combinemulticast messages associated with the given multicast message that arereceived from the second sector and the at least one neighboring targetsector.
 17. The apparatus of claim 8, wherein the logic configured toattempt continues to attempt to monitor until (i) the access terminalcannot decode multicast packets associated with the given multicastsession, an application layer cannot sufficiently correct errors in thegiven multicast session or a packet error rate reaches an unacceptablelevel, or (ii) a second scheduling message is received within the secondsector that advertises the given multicast session as carried in thesecond sector, and further indicates how an access terminal can tune tothe given multicast session in the second sector.
 18. The apparatus ofclaim 8, wherein the first scheduling message corresponds to a broadcastoverhead message (BOM).
 19. The method of claim 1, further comprising:starting a timer after handing off from the first sector to the secondsector; and in response to the attempting failing to monitor themulticast messages associated with the given multicast session in thesecond sector prior to expiration of the timer, stopping the refrainingby transmitting the registration request for the given multicast sessionwithin the second sector.
 20. The method of claim 1, wherein, based uponthe first scheduling message, the attempting occurs after the handoffwithout waiting for any scheduling messages to be received within thesecond sector.